Optical components in optical communication networks need to operate over a wide range of power levels, varying from those emanating from high power sources and amplifiers that may be tens of watts to signals of fractions of microwatts arriving at receivers for detection. Moreover, there is often the need in such networks for a wide dynamic range of optical power sources and receivers. For example, in wavelength division multiplexed (WDM) systems, the power needs are dependent on the number of channels present at a particular time in a WDM system. Also fixed optical attenuators are frequently used to add attenuation to short optical fiber spans to reduce the power impinging on the receiver's detector and variable attenuators have been proposed for use in WDM networks to regulate the signal power to a level appropriate to the number of channels then active.
It is important for a variable optical attenuator to add little excess insertion loss when the signal power is already as low as desirable.
It is also important for a variable optical attenuator to be able to respond rapidly to sudden increases in power levels since excessive power levels that are allowed to persist too long often can do considerable damage or otherwise impair operation.
The present invention provides a variable optical attenuator that should be able to meet these various requirements. In particular, the invention provides a variable power attenuator that is especially useful for power regulation.
The invention involves the use of a novel micro-electro-mechanical system (MEMS) device to provide control of the attenuation. MEMS technology is now a well-recognized technology. Basically, it involves forming a multilayer structure by sequentially depositing and shaping on a silicon substrate a plurality of polysilicon layers that are separated by layers of silicon oxide and/or silicon nitride. The shaping of the layers is generally done by the techniques used in the manufacture of silicon integrated circuits and generally involves the patterning of the layers by photolithographic techniques. The basic principles of MEMS technology are described in a paper entitled "MEM'S the Word for Optical Beam Manipulation" that was published in Circuits and Devices, July 1997, pp. 11-18. MEMS devices are available from many sources, such as, for example, the MEMS Technology Application Center at North Carolina (MCNC) that custom makes devices on order.
Various applications of MEMs devices are described in copending application Ser. No. 09/088,182, filed Jun. 1, 1998 by five of the present applicants and having a common assignee.